Wound Healing Inhibition Factors - Donkey

In clinical practice healing can be achieved in one of three ways:

• Primary or first intention healing.
• Secondary or second intention healing.
• Delayed primary healing.

Primary or first intention healing

This is the mechanism that occurs when the edges of a wound can be closely apposed. Most surgical wounds rely upon this mechanism. In a non-infected surgical wound, healing is reliably accomplished in a predictably short time (usually 7 to 14 days).

Elective surgical wounds are probably the current ‘gold standard’ of wound management, but there are major differences between surgical wounds and accidental injuries (see Table 1 and Table 2 below) and so there are almost inevitable differences in healing between the surgical situation and the accidental wound.

(Image courtesy of The Donkey Sanctuary)

(Image courtesy of The Donkey Sanctuary)

In primary wound healing, the various tissue structures involved are managed by suturing to restore very close normal anatomical relations. The underlying tissues are closed carefully to minimize dead space, provide good support for the skin wound itself and to restore function as far as possible. Although in most cases this will involve closure of the wound by sutures or staples, this is not a prerequisite. Close apposition of the margins of the wound using adhesive tabs or even simply by bandaging in a suitable fashion may have the same effect and may indeed be considered to be advantageous in that there is no foreign matter in the wound. Minimal granulation tissue formation and epithelial migration are required and so the wound heals rapidly. Usually within seven to ten days the wound margin is sufficiently strong to permit removal of skin sutures.

Few accidental/ traumatic wounds are amenable to this approach because there are almost always some complicating factors. Where it is possible however to create a ‘surgical’ situation from a traumatic injury, wounds will heal with an excellent result both functionally and cosmetically.

Secondary or second intention healing

Second intention healing is the natural way for a wound to heal. Wounds too extensive or contaminated to suture, or those in which primary closure has failed, must heal in this way.

In second intention healing, a healthy bed of granulation tissue is required before epithelialisation can proceed. The quality of the granulation tissue bed and the anatomical site has a strong influence on the rate of healing of the wound. Because there is a necessary delay in the development of the granulation tissue bed, there is an inevitable delay in healing.

Major factors in the process of second intention healing are the size of the wound, the anatomical location and the extent of complicating factors:

• Over 70% of donkey wounds are complicated by failure to heal and chronic inflammation
• Second intention healing relies upon the inflammatory response; the longer the wound takes to heal, the greater will be the scar and the possible cosmetic and functional deficits
• The anticipated problems associated with second intention healing may encourage clinicians to try to close wounds by primary union, although this can be ill-advised

Most traumatic wounds create circumstances that preclude primary closure and so second intention healing is a major clinical aspect of wound management in donkeys. Factors that disturb normal corrective processes inevitably complicate and delay wound healing. Early recognition of healing difficulties allows prompt correction; ideally factors that will result in non-healing should be recognized pre-emptively at the time of wounding, but inevitably some will not be apparent until later and possibly when the wound has failed to heal.

The owner of a donkey with one or more of these factors can be given rational advice on the likely prognosis and the time-scale for healing. Most non-healing wounds are preventable by suitable management in the early stages after injury and others are understandable or predictable. Failure to recognize potential reasons for failure of healing in a fresh wound, or delayed presentation, mean that the wound will become chronically inflamed and so the healing process will be unnecessarily prolonged.

Delayed primary healing

This is a useful procedure that combines the early stages of second intention healing with a primary intention healing after a few days. It is applicable to a few wounds but it is a very rewarding process. If closure is delayed for 72 to 96 hours, only a minimal risk of infection exists. The method allows contaminated wounds in which immediate closure may lead to infection to heal faster than would be the case for second intention healing. The wound is initially cleaned and debrided, but is not closed. After a variable time (usually two to four days), the wound is surgically debrided to remove any demarcated tissues and closed by suture as for first intention healing. There is an inevitable delay in the healing process but, where it is applicable, the healing time is usually shorter than second intention healing.

The 'clinical advantages of delayed primary healing are considerable:

• The wound can be assessed for causes of failure of healing at various stages, allowing the best time for closure to be chosen
• Acute inflammatory responses and natural debridement can take place before it is ‘driven’ towards healing without the development of a difficult and prolonged chronic inflammatory process

The disadvantages include the need for repeated procedures and an inevitable increase in scarring when compared to first intention healing, even when the time delay is relatively insignificant.

References

• Knottenbelt, D. (2008) The principles and practice of wound mamagement In Svendsen, E.D., Duncan, J. and Hadrill, D. (2008) The Professional Handbook of the Donkey, 4th edition, Whittet Books, Chapter 9

WOUND MANAGEMENT - DONKEY